Electroluminescent image amplifier



1965 E. w. VAUGHN ETAL. 3,210,551

ELECTROLUMINESCENT IMAGE AMPLIFIER Filed April 18, 1952 and Glass Transparent Conductor Eiectoluminescent (Zn S) High Resisiunce Phoioconductor Canducior Flg. 2.

Lead Glass 1 Transparent Conducior Electroluminescent (Zn 3) High Resismnce Phoioconducior 2 Transparent Conductor 3 leciroluminescem (Zn 5) 5 ugh Resistance 6 Photoconductor Conductor Fug. 4.

WITNESSES: E INV E NJI'OJRS h vere an n fl Edward L. W bib Martin E. Hayes United States Patent 3,210,551 ELEETROLUMHNESQENT IMAGE AMPLIFIER Everett W. Vaughn, Ellicott City, and Edward L. Webb and Martin E. Hayes, Baltimore, Md, assignors to Westinghouse Electric Corporation, East Pittsburgh,

Pa., a corporation of Pennsylvania Filed Apr. 18, 1952, Ser. No. 283,094 29 Claims. (Cl. 250-213) Our invention relates to image intensifiers and in particular relates to an arrangement using the property of electroluminescene to obtain a light-image which is an intensified replica of the space-distribution of a field of radiation. One example of this would be to produce a light-image on a screen showing a body subjected to X- rays which is many times brighter than the picture of the same body produced by a conventional X-ray fluoroscope.

Electroluminescene is the property which some bodies have of emitting light While subject to a varying voltagegradient. Examples of this are properly processed zinc sulphide, cadmium sulphide and silicon carbide. The brightness of the light at any point is approximately proportional to the rate of change of the voltage gradient at any instant, and of course the light disappears when the voltage-gradient ceases to change.

One object of our invention is to provide an improved arrangement for producing a light-image which shall vary from point-to-point in correspondence with the variation point-by-point over the cross-section of a field of projected radiation.

Another object of our invention is to provide an improved device for generating a light-picture corresponding in intensity point-by-point with the transmission by a body subjected to irradiation by an X-ray tube.

Another object is to provide an X-ray image intensifier of a novel type and higher resolving power than was attained by the prior art.

Still another object is to provide a device capable of producing on its output screen a replica in greatly enhanced brightness of a pulsed light-image on its input screen.

Still another object is to provide a light-amplifier which can be superposed on the viewing-screen of an X-ray fluoroscope to give a replica in much greater brightness of the image on that viewing screen.

Other objects of our invention will become apparent upon reading the following description taken in connection with the drawings, in which:

FIGURE 1 is a showing partly diagrammatic and partly structural of an image intensifier embodying our invention applied to an X-ray apparatus;

FIG. 2 is an enlarged detail sectional view of a portion of the structure of FIG. 1;

FIG. 3 is a schematic diagram of apparatus embodying the application of our invention to amplifying the brightness of a light-picture; and

FIG. 4 is a section similar to FIG. 2 of a modification of our invention in which two intensifying units are cascaded.

Referring in detail to the drawings, a screen I preferably of lead glass is coated with a layer 2 of a fairly conductive material which is transparent to light of the wave-length generated by time-varying the voltage-gradient in a layer 3 of electroluminescent material. To give specific examples, the layer 2 may be of the material sold under the trade-name NESA and the layer 3 of zinc sulphide processed to render it electroluminescent as described in an article by Destriau in the Philosophical magazine for October 1947, vol. 38, page 700, and entitled The New Phenomenon of Electrophotoluminesice cence and Its Possibilities for Investigation of Crystal Lattices.

The electroluminescent layer 3 is coated with a highresistance layer 4 which may, for example, be carbon applied very thin. The high-resistance layer 4 may be coat ed with a layer 5 of photoconductive material, which may, for example, be cadmium sulphide applied as described by R. E. Aitchison in the science periodical Nature No. 4255, May 19, 1951, pages 812 and 813. The surface of the photoconductive layer 5 is coated with a conductive coating 6 which preferably has low absorption for X-rays and may, for example, be evaporated aluminum.

The entire structure so far described may be enclosed within a suitable container 7 which may if desired be evacuated. The layers 2 and 4 are connected together and to one pole of a direct-current voltage source 8 by a lead-in wire 9. The other terminal of source 8 is connected by a lead-in wire 11 to the conductive layer 6.

While it will usually be desirable to use this apparatus in environments of low illumination, it will usually be desirable to form the walls of container 7 except at plate 1 of light-opaque material transparent to X-rays, and to make the high-resistance layer 4 opaque to light also. For X-ray image intensifying, the layer 5 is positioned to intercept the radiation transmitted through an object 12 from an X-ray tube 13.

The mode of operation of the FIG. 1 arrangement is as follows.

To use the apparatus for image-intensification it is set up in a darkened room so that initially little or no radiation is incident on the photoconductor layer 5 and the latter has a high and fairly uniform resistance at all points. The electroluminescent layer 3 is then subjected to a steady voltage-gradient at all points and remains substantially dark all over until radiation is incident on the apparatus.

When the FIG. 1 assembly is irradiated by X-rays, or other radiation, through the casing 7, photons will strike various local areas scattered over the photoconductor layer 5. When a photon is absorbed in layer 5, it will greatly increase the electrical conductivity of the latter, but only over a small area of screen surface in its immediate vicinity because the photoconductive substances usually take the form of small crystals when deposited in layers and the effect of the photon is limited by the crystal boundaries. We will hereafter refer to this small area as the stimulus-area. For example, if cadmium sulphide formed as described in the Aitchison article above-mentioned is used for layer 5, the stimulus area for an X-ray photon of the wave-length used in clinical fluoroscopy will probably be of the order of 2 l0 square centimeters. If, however, a photoconductive material is used in which the stimulus-area is not thus limited sufficiently to give a fine-grained picture, the photoconductive material may be deposited, not as an undivided layer but as a mosaic of discrete particles. In this case the conductive layer 6 may still be deposited by conventional methods and will extend from particle to particle. Usual methods of depositing photoconductive substance with which we are acquainted naturally result in discontinuous structure as a matter of fact.

The increase of conductivity in the stimulus-area of layer 5 results in a change of current and voltage-distribution on the high-resistance-layer 4, and a. corresponding sudden jump in voltage gradient in the portion of electroluminescent layer 3 immediately contiguous to the point of incidence of the photon. This sudden change of voltage-gradient in layer 3 causes a spot of light to appear briefly adjacent the incident photon. This. spot soon disappears of course as the conductivity-increase produced in stimulus-area of layer 5 by the photon decays, and as the voltage-gradient in electroluminescent layer 3 stabilizes. Each photon thus produces its brief luminosity adjacent its point of impact, and the combined effect on the eye of an observer looking through glass plate 1 is a picture of the intensity-distribution of the radiation field.

It will be noted that it is the rate-of-change of voltagegradient in layer 3 which produces light and that the incident radiation produces results only because of its quantum aspects. If the separate quanta incident on a stimulus area followed each other before the photo-conductivity in layer had time to decay substantially, the voltagegradient in electroluminescent layer 3 would undergo no time-variation after incidence of the first photon, and only the latter would produce a light-flash in electroluminescent layer 3. Calculation shows that in visible light of perceptible intensities the photons incident on each stimulus-area follow each other at such close intervals that no perceptible light is produced in the electroluminescent layer 3. This difiiculty can be overcome by periodically interrupting or pulsing the light, as by the light-chopper l4 acting on light from source transmitted through picture 16 in FIG. 3.

However, calculation also shows that in the X-rays used in clinical fluoroscopy about 200 photons per second would strike each stimulus-area at the X-ray intensities present in abdominal studies. This timing of 200 per second is well within the saturation period of the order of 10 second estimated for the screen materials mentioned above. Hence for X-ray fluoroscopy the arrangement we have described should operate successfully without any need for artificially pulsing the radiation.

Where the incident radiation to be intensified is of visible wave-length the portions of enclosure 7 and layer 6 which it must traverse to reach photoeonductor layer 5 must of course be transparent to it rather than merely to X-rays; otherwise the device utilizing visible radiation may be as described above. Since television receiver pictures and motion-pictures consist of pulsed light the modification now under discussion may be used to intensify such pictures without requiring the light-chopper 14. It will be noted that since the light generated in the electroluminescent layer 3 is pulsed in character one or more light-intensifiers of the type shown in FIG. 2 may be interposed between the transparent conductor 2 and the glass plate 1, as shown in section in FIG. 4, thereby cascading the intensifying power of each intensifying unit any desired number of times.

Since the light on the screen of an ordinary fluoroscope is pulsating by reason of its generation by X-ray photons, an intensifier for light fields like the tube described for FIG. 1 may be used to intensify the image on the fluorescent screen. Unless an optical system to focus the image of the fluoroscope screen on the photoeonductor layer 5 of the intensifier is to be used, the spacing between the conductor layer 6 and the outside face of casing 7 should be designed to be as small as possible however.

It may be noted that the zinc sulphide as treated to be electroluminescent has a high resistivity. Advantage might arise in certain field of use if this material were made a little more electroconductive, for example by a proper admixture of other material such as possibly tin oxide, inasmuch as this would help localize the voltage gradient adjacent the stimulus-area. In some cases where this was done, the high resistance layer 4 could be dispensed with.

If the high-resistance layer 4 be made transparent to the light generated in electroluminescent layer 3, the feedback of this light to photoeonductor 5 would have a regenerative effect which might be desirable in intensifying certain types of image.

We claim as our invention:

1. A radiation image transformer comprising a group of layers superposed in the following order and consisting of: a light-transparent conductive layer, an electroluminescent layer, a high-resistance layer, a photoconductive layer and a low-resistance layer which is transparent to said radiation; and an enclosure means containing said group which is opaque to light except on a wall-portion facing said light-transparent conductive layer.

2. A radiation image transformer comprising a group of layers superposed in the following order and consisting of: a light-transparent conductive layer, a layer of zinc sulphide, a high-resistance layer, a layer of cadmium sulphide and a low resistance layer which is transparent to said radiation; and an enclosure means containing said group which is opaque to light except on a wall-portion facing said light-transparent conductive layer.

3. A radiation image transformer comprising a group of layers superposed in the following order and consisting of a light-transparent conductive layer, a layer of zinc sulphide processed to render it electroluminescent, a highresistance layer, a layer of cadmium sulphide and a lowresistance layer which is transparent to said radiation; and an enclosure means containing said group which is opaque to light except on a wall-portion facing said lighttransparent conductive layer.

4. A radiation image transformer comprising a group of layers superposed in the following order and consisting of: a light-transparent conductive layer, an electroluminescent layer, a high-resistance layer, a photoconductive layer and a low-resistance layer which is transparent to said radiation; and an enclosure means containing said group.

5. A radiation image transformer comprising a group of layers superposed in the following order and consisting of: a light-transparent conductive layer, an electroluminescent layer, a high-resistance layer, a photoconductive layer and a low-resistance layer which is transparent to said radiation; and an enclosure means containing said group, said high-resistance layer being opaque to the light of said electroluminescent layer.

6. A radiation image transformer comprising a group of layers superposed in the following order and consisting of: a light-transparent conductive layer, an electroluminescent layer, a high-resistance layer, a photoconductive layer and a low-resistance layer which is transparent to said radiation; and an enclosure means containing said group which is opaque to light except on a wall-portion facing said light-transparent conductive layer, said highresistance layer being opaque to the light of said electroluminescent layer.

7. A radiation image transformer comprising a plurality of groups of layers superposed in the following order and consisting of an electroluminescent layer having one face in contact with a light-transparent conductive layer, and its other face in contact with a high-resistance layer, a photoconductive layer having one face in contact with a low-resistance layer which is transparent to said radiation and its other face in contact with said highresistance layer, and an enclosure means containing said group which is opaque to light except on a wall-portion facing said light-transparent conductive layer.

8. A radiation image transformer comprising a plurality of groups of layers superposed in the following order and consisting of: a light-transparent conductive layer, an electroluminescent layer, a high-resistance layer, a photoconductive layer and a low-resistance layer which is transparent to said radiation; and an enclosure means containing said groups.

9. A radiation image transformer comprising a plurality of groups of layers superposed in the following order and consisting of a light-transparent conductive layer, a layer of zinc sulphide, a high-resistance layer, a layer of cadmium sulphide and a low resistance layer which is transparent to said radiation; and an enclosure means containing said groups which is opaque to light except on a wall-portion facing said light-transparent conductive layer.

10. A device for visualizing X-ray images comprising a group of layers superposed in the following order and consisting of a light-transparent conductive layer, an electroluminescent layer, a high-resistance layer, a photoconductive layer, and a low-resistance layer which is transparent to X-rays; an enclosure means containing said group, and means to project X-ray image-fields into incidence with said photoconductive layer.

11. A device for visualizing X-ray images comprising a plurality of groups of layers superposed in the following order and consisting of a light-transparent conductive layer, an electroluminescent layer, a high-resistance layer, a photoconductive layer, and a low-resistance layer which is transparent to X-rays; an enclosure means containing said groups, and means to project X-ray image-fields into incidence with said photoconductive layer.

12. A device for visualizing X-ray images comprising a group of superposed layers in the following order and consisting of a light-transparent conductive layer, a layer of zinc sulphide processed to render it electroluminescent, a high-resistance layer, a layer of cadmium sulphide, and a low-resistance layer which is transparent to X-rays; and means to project X-ray image-fields into incidence with said cadmium sulphide layer.

13. A device for visualizing radiation images comprising a group of superposed layers in the following order and consisting of a light-transparent conductive layer, a layer of zinc sulphide processed to render it electroluminescent, a high-resistance layer, a layer of cadmium sulphide, and a low-resistance layer which is transparent to said radiation; and means to project said radiation into incidence with said cadmium sulphide layer.

14. A device for visualizing radiation images comprising a plurality of groups of layers superposed in the following order and consisting of a light-transparent conductive layer, an electroluminescent layer, a high-resistance layer, a photoconductive layer, and a low-resistance layer which is transparent to said radiation; an enclosure means containing said groups, and means to project said radiation into incidence with said photoconductive layer.

15. A radiation image transformer comprising a group of layers superposed in the following order and consisting of: a light-transparent conductive layer, a Zinc sulphide layer, a high-resistance layer, a cadmium sulphide layer and a low-resistance layer which is transparent to said radiation; and an enclosure means containing said group.

16. A radiant energy image intensifier comprising the combination of a stratum of material, the electric impedance of which is subject to change by radiant energy excitation, a stratum of electro-luminescent material, means for supporting said respective strata in contiguous position, means for impressing an electric field on said strata.

17. The method of producing an intensified optically visible image corresponding to a radiant energy image comprising the following steps: (a) arranging particles of a material which will change in electrical resistivity when irradiated with radiant energy as a panel of desired spatial configuration and closely adjacent to one another, (b) arranging a second panel of an electroluminescent phosphor substantially coextensive with and in close proximity to said first panel of particles, (0) setting up an electric field between said panels, and, (d) subjecting said first-mentioned panel to radiant energy whereby resulting changes in electric field distribution therein will produce an optically visible image in said second-mentioned panel.

18. A radiant energy image intensifier comprising a film of luminescent phosphor, a transparent support therefor, a layer of cadmium sulfide adjacent to and substantially coextensive with said phosphor, means for making electrical contact respectively with said phosphor film and said sulfide layer and means for impressing an electric field upon said electric contacts.

19. The method of reproducing, as a visual image, variations of a radiant energy beam which consists in causing said variations to initiate corresponding variations of electric impedance in a body of cadmium sulfide, impressing a high frequency electric field on said body, and exposing an electroluminescent material to the resulting pattern of electric field variations whereby a corresponding and intensified visual pattern is produced.

20. A dielectric assembly for use in a radiation amplifier comprising two elements of dielectric material in series arrangement, one element including electroluminescent material, the other element including a plurality of operatively isolated masses of photo-conductive material, said masses constituting electrically independent impedances in series arrangement with said one element.

21. A radiation-handling device comprising two elements of dielectric material electrically in series, one element including electroluminescent material, the other element including a plurality of operatively isolated masses of photosensitive material, said photosensitive material having impedance characteristics which vary in response to varying intensity of incident radiation, said masses constituting electrically independent impedances in series arrangement with said one element, and means for applying an electric field in series with said two elements.

22. An image intensifying X-ray fluoroscopic screen comprising a layer of X-ray sensitive light emitting material having a characteristic emission when excited by incident X-rays, a visible light amplifying cell contiguous with said X-ray sensitive material, said light amplifying cell having a peak sensitivity to the characteristic emission of said X-ray sensitive material, and means for impressing an electrical potential difference between opposite surfaces of said light amplifying cell.

23. An image intensifying X-ray fluoroscopic screen comprising a layer of X-ray sensitive light emitting material which emits visible light within the range of 4000 to 5500 Angstrom units when excited by incident X-rays, a visible light amplifying cell contiguous with said X-ray sensitive material, said light amplifying cell having a peak sensitivity to substantially the same wavelength light as is emitted by said X-ray sensitive material, and means for impressing an electrical potential difference between opposite surfaces of said light amplifying cell.

24. An image intensifying X-ray fluoroscopic screen comprising a layer of X-ray sensitive and visible light emitting material having a characteristic emission when excited by X-rays, a first transparent conducting film overlying said X-ray sensitive layer, a layer of a photoconductive material having a peak photoconductive sensitivity to the characteristic emission of said X-ray sensitive layer overlying said first transparent conducting film, a layer of opaque non-conducting material. overlying said photoconductive material, a layer of electroluminescent phosphor overlying said opaque layer, a second transparent conducting layer overlying said electroluminescent layer, a transparent supporting base plate contacting said second transparent conducting film, and means for impressing an electrical potential difference between said first and second transparent conducting films.

25. A radiation amplifier comprising an elemental layer of photoconductive material having impedance characteristics dependent upon incident radiation, an elemental layer of electroluminescent material disposed substantially parallel to said photoconductive layer, conductive means interconnecting both elemental layers, an electrode terminal conductively connected to said photoconductive layer, the portions of said means and said terminal which contact said photoconductive layer being physically spaced apart whereby said photoconductive layer is series connected therebetween, and an electrode terminal for said electroluminescent layer, both electrode terminals being so arranged that an electric field connected thereto will distribute over both layers in accordance with the respective impedances thereof.

26. A radiation amplifier comprising an elemental layer of photoconductive material having impedance characteristics dependent upon incident radiation, an elemental layer of electroluminescent material disposed substantially parallel to said photoconductive layer, a contact element having one surface conductively engaging said electroluminescent layer, an electrode terminal conductively connected to said photoconductive layer, said element and said terminal being conductively connected to said photoconductive layer at spaced apart points whereby the latter is connected in series therebetween, and an electrode for said electroluminescent layer, both electrode terminals being so arranged that an electric field connected thereto Will distribute over both layers thereof.

27. A radiation amplifier comprising a transparent reinforcing member which admits incident radiation therethrough, an elemental layer of photoconductive material having impedance characteristics dependent upon incident radiation and carried by said member, said layer being disposed in a plane normal to the path of said radiation, an elemental layer of electroluminescent material disposed substantially parallel to said photoconductive layer, a contact element having one surface conductively engaging said electroluminescent layer, an electrode terminal conductively connected to said photoconductive layer, said element and said terminal contacting said photo conductive layer at spaced apart points whereby the latter is connected in series therebetween, and an electrode for said electroluminescent layer, both electrode terminals being so arranged that an electric field connected thereto will distribute over both layers in accordance with the respective impedances thereof.

28. A radiation amplifier comprising a transparent reinforcing member which admits incident radiation therethrough, an elemental layer of photoconductive material having impedance characteristics dependent upon incident radiation and carried by said member, said layer being disposed in a plane normal to the path of said radiation, an elemental layer of electroluminescent material, an elemental contact having a surface area conductively engaging said electroluminescent layer, means conductively coupling said contact with said photoconductive layer, a voltage-applying terminal engaging said photoconductive layer at a point spaced from said means whereby said photoconductive layer is connected in series therebetween, and a voltage-applying terminal for said electroluminescent layer, both terminals being so arranged that an electric field connected thereto will distribute over both layers in accordance with the respective impedances thereof.

29. A radiation amplifier comprising a transparent reinforcing member having parallel opposite faces, a layer of photoconductive material having impedance characteristics dependent upon incident radiation and disposed on one of said faces, a first voltage-applying terminal carried by said one face in contact with said photoconductive layer, a layer of electroluminescent material, a flat contact element having one surface in contact with said electroluminescent layer, a conductive member in contact with said photoconductive layer and said element, said conductive member contacting said photoconductive layer at a point spaced from the contact of said terminal with said photoconductive layer whereby the latter is connected in series therewith, and a second voltage-applying terminal on said electroluminescent layer opposite said contact element whereby an electric field applied to both terminals will distribute over said layers in accordance with the respective impedances thereof.

References Cited by the Examiner UNITED STATES PATENTS 2,239,887 4/41 Ferrant 25071 X 2,566,349 9/51 Mager 250-71 X 2,603,757 7/52 Sheldon 250 X 2,650,310 8/53 White 250-71 OTHER REFERENCES New Phenomenon of Electrophotoluminescence, from The Philosophical Magazine, October 1947, pp. 7117l3.

RALPH G. NILSON, Primary Examiner.

ELI J. SAX, Examiner. 

1. A RADIATION IMAGE TRANSFORMER COMPRISING A GROUP OF LAYERS SUPERPOSED IN THE FOLLOWING ORDER AND CONSISTING OF: A LIGHT-TRANSPARENT CONDUCTIVE LAYER, AN ELECTROLUMINESCENT LAYER, A HIGH-RESISTANCE LAYER, A PHOTOCONDUCTIVE LAYER AND A LOW-RESISTANCE LAYER WHICH IS TRANSPARENT TO SAID RADIATION; AND AN ENCLOSURE MEANS CONTAINING SAID GROUP WHICH IS OPAQUE TO LIGHT EXCEPT ON A WALL-PORTION FACING SAID LIGHT-TRANSPARENT CONDUCTIVE LAYER. 